The first thing that is important to understand about the Tentatek is that it succeeds under the presence of momentum. This weapon is not really meant to get the opening kills that allow your team to push, and instead gets kills to sustain a push. Flanking 24/7 is not really advised. You can get away with it in solo queue because... it's solo queue... but focus on objective primarily and flank secondarily. Watch a few streams and see how the weapon is played at a high level. Compare the footage to how you play, make notes and focus on improving those weaknesses. The rest is honestly just grinding the weapon.
In terms of kits, the Tentatek has the luxury of being one of if not the most gear-independent weapon in the game. So you have some freedom to use what you want. The kits that I most often use are down below... Your kit's primary focus should be mobility, then either ink management (no more than a main of ink recovery is necessary), or special perks. If fall-off is annoying to you, add a main of damage. Don't bother countering defense up, it isn't worth it. Defense builds are also good, I just personally don't enjoy them.